Crown ether functionalization of a porphyrin-based “molecular square”: induction of fluorescence sensitivity to alkali metal cations

A porphyrin-based “molecular square” (1), prepared by reaction of a dipyridylporphyrin species with Re(CO)5Cl and subsequently with ZnII acetate, was functionalized with 2-(methylene-15-crown-5-ether)-nicotinoyl ester (2). Functionalization was achieved by axially ligating each of the four available ZnII sites within the porphyrins. (2) was synthesized by reaction of 2-(hydroxymethyl)-15-crown-5-ether and nicotinoyl chloride in CH2Cl2. Functionalization renders the square’s fluorescence emission intensity responsive to added Na+ and, to a lesser extent, K+.